This invention relates to arrangements for introducing air into a body of wastewater, such as an activated sludge basin, in which an aerator is suspended below the surface of the water by a float associated with an air supply line.
Such floating aerator arrangements are described, for example, in the U.S. Pats. to von Nordenskjold Nos. 4,287,062 and 4,797,212. As described in those patents, the introduction of air into a basin containing wastewater by floating aerators of this type, particularly for the clarification and biological purification of the wastewater in socalled activated sludge systems, produces a very effective cleaning of the basin with a very low energy expenditure. The floating aerator arrangements described in those patents include lines of aerators that are spaced from each other, extending across the part of the basin to be aerated, so that the lines, which are at the surface of the water, move laterally in a reciprocating manner. Tubes extending downwardly from the aerator lines supply air from them to the aerators suspended below the surface of the water.
When the term "air" or "aeration" is used herein, that term includes, in general, gases such as oxygen and also gas mixtures and the introduction of them into the water for special applications. When the term "water" is used herein, that term includes all types of liquids which may be processed by air or aeration.
As a result of the reciprocating movement of the air supply lines, the suspended aerators also move back and forth below the water surface and thus move through the entire volume of water in the aerated portion of the basin, which results in a very uniform introduction of oxygen into the water. The travelling movement of these air lines with suspended aerators, which are also referred to as "aerator chains", results from the introduction of air through the suspended aerators, so that no external driving force is required. For further details regarding this action, reference can be made to the above-mentioned United States patents which are incorporated herein by reference.
In those prior art aeration systems, the air supply lines in the aerator chains consist of hose sections, and the aerators are suspended from T-shaped tube members having horizontal arms to which the hose sections are connected and a vertical leg leading to the suspended aerator, along with floats attached to the T-shaped tube members or to the adjacent ends of the hose sections. The hose sections, which extend between adjacent T-shaped tube members, are attached to the arms of those members by hose clamps or the like in a conventional manner.
Although this arrangement has proved effective to produce a reciprocating movement of the floating aerators with the resulting biological cleaning action, it has been found that the float arrangement could be improved. In many instances, the aeration chains containing the floating aerators must be quite long, for example, 30-50 meters, in order to extend from one side of a basin to the other side. As a result, not only during assembly but also in operation, considerable forces are applied to the joints between the flexible hose sections of the air supply line and the T-shaped tube members where the floats are provided. This may cause damage to those joints so that the air lines become leaky and ultimately fail at these points, for example, by being completely torn apart. As a result, the operation of the entire floating aerator chain is terminated, which endangers the operation and biology of the whole aeration system in the basin and frequently leads to a complete breakdown in an irreparable manner, requiring the activated sludge to be built up again in a lengthy process. Moreover, the repair of damaged joints is laborious, because it is necessary either to drain the water from the basin or to use rubber dinghies or the like in order to reach the joint locations and carry out the necessary repairs. A very particularly disadvantageous result is caused by sludge entering the air lines following separation, which can lead to blockages of the lines.
A further disadvantage is that, during any such on-site repair, there is danger of injury to the person carrying out the repair. In particular, during tightening of the hose clamps at the connecting points, minor injuries may occur as a result of slippage of a screwdriver or from the edges of the projecting straps of the hose clamps, which is particularly dangerous because systems of this type contain large concentrations of harmful bacteria, which can lead to blood poisoning or the like in the worker.
Furthermore, in some cases, the floats are formed as a foam body which is injection-molded around a tubular T-shaped section which must be completely lined with tar or the like, resulting in a very expensive manufacturing process.